1. Field of the Invention
The present invention relates to improved prestressed concrete tanks and their construction and, more particularly, relates to elongated prestressed concrete tanks which may be designed and adapted for more efficient utilization of the area of construction site.
2. Description of the Prior Art
The present invention is particularly useful in connection with prestressed composite tanks. Such tanks are widely used for storage of liquid and similar purposes and normally include a light gauge steel shell diaphragm which is encased in layers of a cementitious material such as shotcrete. While these tanks have become known as prestressed concrete tanks, the term concrete is used generically and in practice includes shotcrete (which may contains small rocks). The shotcrete utilized in the construction of prestressed composite tanks is generally applied by a pressure gun and thus rocks of any substantial size cannot be tolerated. The cementitious material that is utilized in connection with the present invention, generally consists of a mixture of cement, sand and water, although small rocks might be incorporated into the mixture so long as the same are small enough to flow through the nozzle of the gun.
The prestressed composite tanks which are known have generally been of circular construction. Thus, after the steel shell is encased in layers of a cementitious material, the outer periphery may be wrapped with prestressing wire which, after tightening, is enclosed by a cover coating of shotcrete. Stretching or tightening of the wire imposes centripetal forces on the wall of the tank and thus, due to the circular configuration of the wall, the entire wall is placed into circumferential compression. Such prestressed tanks and a method for producing the same are disclosed in United States Letters Pat. No. 3,822,520 which is owned by the assignee of the present application.
The '520 patent also discloses a method for sealing the joints between adjacent panels of the steel shell. This method involves forming joints so that they provide a hollow channel which runs vertically of the joint, and thereafter pumping the channel full of a sealant. This method for sealing panels is utilized in the preferred tanks and construction methods of the present invention and the entirety of the disclosure of the '520 patent is hereby specifically incorporated by reference.
As set forth above, prestressed composite tanks have traditionally been circular so that prestressing is accomplished simply by pulling a prestressing wire all the way around the tank to thereby place the entire circumferential extent of the wall into circumferential compression. Moreover, it has been known to wrap a single wire spirally around the tank so that a significant vertical portion of the tank may be prestressed with a single wire. Such methods are well known and have been utilized for a long period of time and such prestressing methodology is fully disclosed and described in U.S. Pat. No. 2,370,780, the entirety of the disclosure of which is also hereby incorporated by reference.
The fact that known prestressed composite tanks are circular has been a problem in the industry on construction sites that are not of a size and shape to efficiently facilitate and accommodate circular tanks, particularly when large gallonages are required. That is to say, long and narrow sites may not accommodate the construction of a circular tank of the required size. Accordingly, the use of elongated tanks which might more efficiently be fitted into the construction site have been suggested. However, elongated tanks by necessity include elongated straight wall sections, which until the present invention, were subject to cracking from shrinkage during curing and hardening of the cementitious material.